Many processes used in semiconductor manufacturing involve the use of metal containing chemicals, or their solutions, for the purpose of depositing thin metallic films onto silicon wafer surfaces. Examples include the use of tungsten hexafluoride for tungsten metallization by Chemical Vapor Deposition (CVD), dimethylaluminum hydride for aluminum deposition by CVD, Cu(hfac)(tmvs) type precursors (where (tmvs) is trimethylvinylsilane and (hfac) is 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate) for thin copper film growth by CVD in addition to aqueous copper containing solutions for either the electroplating or electroless deposition of copper thin films.
Examples of copper and nickel CVD processes are found in U.S. Pat. Nos. 5,085,731; 5,098,516; 5,144,049; 5,187,300; 5,322,712; and U.S. Pat. No. 3,594,216.
In the case of CVD processes there is always a substantial portion of the chemical precursor-that passes through the process chamber unchanged. Typically, this unreacted material, along with the effluent resulting from reacted precursor, must be chemically neutralized or decomposed in an `abatement system` downstream from the process chamber. The resulting material is then disposed of as toxic chemical waste. Examples of common abatement techniques are pyrolytically destructive `burn-box` systems, chemically reactive scrubbers and chemical absorbents. The disposal of these waste materials is both expensive and environmentally unsound, especially in the case of copper since it is known to be a heavy metal contaminant. Disposal of copper containing wastes also occurs with the aqueous copper solutions used in electroplating and electroless copper techniques.
Capture of the byproducts of copper CVD has been suggested in the article, Removal of Byproducts from CVD Copper Effluent Streams, No. 41242, Research Disclosures, (August 1998), pp. 1059-1061, where copper hexafluoroacetylacetonate trimethylvinylsilane ("Cu(hfac)(tmvs)") is the copper CVD precursor which results in copper metal deposition and a by-product mix of unreacted Cu(hfac)(tmvs), Cu(hfac).sub.2 and tmvs. The unreacted Cu(hfac)(tmvs) is converted to Cu(hfac).sub.2 by temperatures of approximately 200.degree. C. to result in an effluent comprised of only Cu(hfac).sub.2 and tmvs. From this mixture solid Cu.sup.+2 (hfac).sub.2 is captured in a cold trap at no greater than 50.degree. C. for reuse.
U.S. Pat. No. 3,356,527 deposits copper from Cu(hfac).sub.2 using hydrogen as a carrier gas and a reducing agent. The resulting Hhfac chelate free ligand is cold trapped and recycled. Similar disclosures are made in: Temple, et. al., Chemical Vapor Deposition of Copper from Copper (II) Hexafluoracetylacetonate, J. Electrochem. Soc. Vol 136, No. 11, November 1989, pp. 3525-3529; Kaloyeros, et. al., Low-Temperature Metal-Organic Chemical Vapor Deposition (LTMOCVD) of Device-Quality Copper Films for Microelectronic Applications, J. Electr. Mat., Vol. 19, No. 3, 1990, pp. 271-276; Van Hemert, et. al. Vapor Deposition of Metals by Hydrogen Reduction of Metal Chelates, J. Electrochem. Soc., Vol. 112, No. 11, November 1965, pp. 1123-1126; and Oehr, et. al., Thin Copper Films by Plasma CVD Using Copper-Hexafluoro-Acetylacetonate, Appl. Phys., A 45, (1988), pp. 151-154.
The present invention overcomes the drawback of abatement and inefficient utilization of chemical components of a copper CVD process by providing a unique process enhancement to recover ligands for reuse and resynthesis of copper CVD precursors as will be set forth in greater detail below.